Hydraulic drive for reciprocating tables



April 1950 J. K. DOUGLAS 2,504,664

HYDRAULIC DRIVE FOR RECIPROCATING TABLES Filed March 27, 1948 3SneetsSheet 1 FIG. 1

INVENTOR JAMES K. DOUGLAS WW ATTORNEY April 8, 1950 J. K. DOUGLAS2,504,664

- HYDRAULIC DRIVE FOR RECIPROCATING TABLES Filed March 27, 1948 3Sheets-Sheet 2 FIG. 2

. I u q INVENTOR I JAMES K DOUGLAS 0| 0 %W% 56 ATTORNEY Apr l, 18,-1-950 J. K. DOUGLAS HYDRAULIC DRIVE FOR RECIPROCATING TABLES Filed March27. 1948 llO- v "2 l9 m us n5 n4 FIG. l2 v 3 s1 s2 53 54 49 4s- 47-2? 552 0 48 z o o 46 56 F|e.l3 49 55 5| 5? 62 53 54 45+ 48/ so 52 o FIG. I4

72 74 1a 70 go FIG. l5 7 3 Sheet -Sheet 3 FIG. 8

FIG. I l

INVENTOR JAMES K. DOUGLAS ATTORNEY Patented Apr. 18, 1950 HYDRAULICDRIVE FOR RECIPROCATING TABLES James K. Douglas, Shorewood. Wis.,assignor to The Oilgear Company, Milwaukee, Wis., a corporation 01Wisconsin Application March 27, 1948, Serial No. 17,415

1 Claims.

This invention relates to hydraulic drives of 1 the type in which a pumpand one or more hydraulic motors are connected into a hydraulic circuitand the flow of liquid in the circuit is intermittently reversed tocause the motor or motors to operate in opposite directions alternately.

The type of drive to whichthe invention relates in particular is adaptedto drive a machine in which work is operated upon by a tool in responseto relative reciprocation between the tool and the work, such as thedrive shown in application Serial No. 6,503 filed February 5, 1948 nowPatent No. 2,499,633, of which this application is a continuation inpart.

For the purpose of illustration, the invention has been shown embodiedin a drive for reciprocating the table or carriage of a planer of thetype in which the work to be machined is fastened to the table and atool or tools carried by a stationary cross-rail takes successive cutsfrom the work during reciprocation of the table but it is to beunderstood that the invention is not limited to a drive for such amachine.

The range of reciprocation of a planer table is determined by two dogswhich are fastened to the table at spaced apart points and which operatea reversing mechanism at each end of the table stroke so that afterbeing started the table will continue to reciprocate within a fixedrange until its movement isstopped or altered by the operator. However,it is necessary at times to move the table beyond its normal range orreciprocation.

In the drive shown in the above application, the table can be started,stopped or reversed, the speed of the table can be varied within a givenspeed range, and the table can be retracted beyond its normal range ofreciprocation by operating a single control element which is arranged atthe operators station. However, the only way to change the speed of thetable is to vary the displacement of the pump.

The present invention has as an object to provide a hydraulic drivewhich has all of the advantages of the drive shown in the aboveapplication.

Another object is to provide a hydraulic drive having means for causingthe table of a ma.- chine to move at selected speeds within any one of aplurality of speed ranges.

Another object is to provide a hydraulic drive having means forpreventing or reducing rebound of the table due to the table jumpingahead in response to the load on the motor being suddenly eliminated orgreatly reduced.

Other objects and advantages of the invention will appear from thefollowing description of a hydraulic drive in which the invention isembodied.

The drive is shown schematically in the accompanying drawings in whichthe views are as follows:

Fig. 1 is a diagram illustrating the fuctional relationship of the partswhich are shown in different planes in order that all hydraulicconnections may be illustrated, the parts being shown in the positionsoccupied when the drive is idle.

Fig. 2 is in part a top plan view and in part a sectional plan view ofthe pump shown in Fig. 1, the pump control, being drawn on a largerscale than the pump proper.

Fig. 3 is a cross-section taken on the line 3-3 of Fig. 2 but drawn to alarger scale.

Figs. 4 and 5 are views similar to Fig. 3 but showing the valve memberin positions difierent from that shown in Fig. 3.

Fig. 6 is a view showing a mechanically op- I ferent from that shown inFig. 1.

Fig. 7 is a view showing a hydraulically operated valve with its plungerin a position dif-. ferent from that shown in Fig. 1.

Figs. 8 and 9 are views showing a speed selector valve with its parts inpositions diflerent from those in Fig. 1.

Figs. 10 and 11 are views showing another speed selector valve with itsparw in positions diflerent from those shown in Fig. 1.

Figs. 12 and 13 are views showing a speed selector pilot valve with itsplunger in positions difi'erent from that shown in Fig. 1.

Figs. 14 and 15 are views showing a circuit unlocking valve with itsparts in position different from those shown in Fig. 1.

For the purpose of illustration, the drive has been shown as beingemployed to reciprocate the table 1 of a planer of conventional type.Since such planers are well known and form no part of the presentinvention, only the table has been connecting piston 3 to the left endof table 1. I

With such a motor, table 1 would be moved toward the left at slow speedwhen the right end of cylinder 2 was supplied with liquid from a pumpand the left end of cylinder 2 was connected to exhaust, it would bemoved toward the left at a higher speed when both ends of cylinder 2were supplied with liquid from the pump, and it would be moved towardthe right when the left end of cylinder 2 was supplied with liquid fromthe pump and the right end thereof was connected to exhaust.

However, when the table was being moved toward the left, the pump wouldhave to draw part or all of its liquid from a reservoir which isobjectionable if a cut is being taken from work in response to movementof the table toward the left. Therefore, the present invention providesan additional stationary cylinder and a ram 6 which extends intocylinder 5 and is connected to the right end of table I. It is to beunderstood that ram 3-4 and ram 6 could be fixed in stationary positionsand cylinders 2 and 5 be fastened to table I which would be anequivalent of the structure shown.

The arrangement is such that when liquid is supplied from a pump to theleft ends of cylinders 2 and 5 and the right end of cylinder 2 isconnected to the intake of the pump, table I will be moved toward theright at a slow speed by the liquid acting upon the end of ram 6 andupon the annular area of piston 3 around rod 4. Piston 3 will ejectliquid from the right end of cylinder 2 and the ejected liquid will flowto the intake of the pump.

When liquid is supplied from a pump to cylinder 5 and both ends ofcylinder 2 are connected to each other and to the intake of the pump,table I will be moved toward the right at high speed by the liquidacting upon the end of ram 6 and piston 3 will eject liquid from theright end of cylinder 2. A part of the ejected liquid will flow to theleft end of cylinder 2 to keep it flooded and the remainder of theejected liquid will flow to the intake of the pump.

When liquid is supplied from a pump to the left end of cylinder 2 andcylinder 5 and the right end of cylinder 2 are connected to each otherand to the intake of the pump, table I will be moved toward the right atan intermediate speed by the liquid acting upon the annular area ofpiston 3 around rod 4 and piston 3 will expel liquid from the right endof cylinder 2. A part of the expelled liquid will flow to cylinder 5 tokeep it flooded and the remainder of the expelled liquid will flow tothe intake of the pump.

When liquid is supplied from a pump to the right end of cylinder 2, theleft end of cylinder 2 is connected to the right end thereof andcylinder 5 is connected to the intake of the pump, table I will be movedtoward the left at high speed by liquid acting upon an area of piston 3equal to the cross-sectional area of rod 4 and the liquid ejected bypiston 3 from the left end of cylinder 2 will flow to the right endthereof so that the pump need supply only a volume of liquid equal tothe displacement of rod 4. The

liquid ejected by ram 6 from cylinder 5 will flow to the intake of thepump.

TableI may thus be moved toward the right on a cutting stroke at eithera high speed, a low speed or an intermediate speed by selecting a ramarea upon which the liquid acts and each of those speeds may be variedby varying the displacement of the pump.

If piston rod 4 and ram 6 have the same crosssectional area, the volumeof liquid returned from the motor to the pump is equal to the volume ofliquid discharged by the pump except for the very small volume lostthrough slip. That is, the small decrease in volume due to leakage andto the compression of the liquid when under pressure.

The hydraulic motor is adapted to be energized by motive liquid suppliedthereto by a pump 8 which is continuously driven when the drive is inoperation and which has two channels 9 and I0 connected thereto. Pump 8may be a unidirectional pump and the flow of liquid between the pump andmotor may be reversed through a, reversing valve but preferably the flowis reversed by reversing the pump.

The liquid discharged by pump 8 is directed to the pressure area on oneside or the other of piston 3 or to the pressure area on ram 6 or to acombination of those areas under the control of two speed selectorvalves II and I2.

Valve II includes a valve body I5 having an axial bore I6 formed thereinand four annular grooves or ports II, I8, I9 and 20 formed in the wallof bore I6. Ports I9 and 20 are connected to each other by a passage 2Iwhich is formed in valve body I5 and terminates in a port 22.

The flow of liquid through valve body I5 is controlled by a valve orplunger 23 which is fitted in bore I5 and urged toward the left by lightspring 24 arranged in the right end of bore I6. Plunger 23 is adapted tobe moved toward the right by a hollow piston 25 which is fitted in acylinder 26 arranged upon the left end of body I5.

Motion is transmitted from piston 25 to plunger 23 by means of a spring21, which is arranged within piston 25, and a push rod 28 which has oneend in engagement with spring 21 and its other end in engagement withplunger 23. Spring 21 has sufficient strength to move plunger 23 towardthe right against the resistance of spring 24.

The right end of cylinder 26 is open to drain at all times and the leftend thereof is adapted to be supplied with motive liquid or to beconnected to drain selectively as will presently be explained. When theleft end of cylinder 26 is open to drain, spring 24 will move plunger 23to its left-hand position as shown in Fig. 10 and then liquid may flowfrom port I! to port 22 When the left end of cylinder 26 is suppliedwith motive liquid, piston 25 will move plunger 23 to its right-handposition as shown in Fig. l and then liquid may flow from port I8 toport 22. When piston 25 is holding plunger 23 to the right and liquidunder pressure is supplied to the right end of bore I6, the liquid canmove plunger 23 to its left-hand position against the resistance ofspring 27 as shown in Fig. 11 and then the liquid can flow from theright end of bore I6 through port H.

In order that springs 24 and 21 may shift plunger 23 from one to theother of its two positions, the left-hand piston on plunger 23 isprovided with one or more slots 29 which permit liquid to escape fromthe left end of bore I6 during the last part of the movement of plunger23 toward the left and through which pressure can extend into the leftend of bore I6 to hydrostatically balance plunger 23 when it is in itsleft-hand position as shown in Fig. 10.

Valve I2 has been shown turned end for end in respect to valve II butthe two valves are identical and they function in the same manner.Therefore, like parts have been indicated by like reference numeralswith the exponent a added to the reference numerals applied to was 8valve I! so that the foregoing m sufllce for both valves.

Port ll of valve Ii is connected to port it of valve If by a channel"which is connected y channel 9 to one port of pump 6. Channel llconnects the other port of pump 6 to the right end of cylinder 2 and itis connected intermediate its ends by a channel 36' to a channel I!which connects port I! of valve II to port l'l of valve l2.

Port 22 of valve II is connected to cylinder I by a channel is which isconnected by a channel 36 to the right end of bore l6. A check valve 40is arranged in channel It between port 22 and channel. 38 to permit flowfrom port 22 into channel 36 and to prevent flow in the oppositedirection. Portji of valve II is connected to the left end of cylinder Iby a channel 4! which is connected by a channel 42 to the left end ofbore I6'-. A check valve 43 is arranged in channel 4| between port 22'and channel '42 to permit flow from port 22" into channel II and toprevent fiow in the opposite direction. I

The left end of cylinder 26 on valve H and the right end of cylinder 26'on valve I: are adapted to be supplied with motive liquid or to beconnected todrain selectively under the control of a manually operablepilot valve 46 which includes a valve body 46 having an axial bore 41formed therein and a valve or plunger 46 fitted in bore 41 and adaptedto be shifted from one to the other of three positions by a hand lever49 connected thereto. I

Plunger 48 controls communication between five annular grooves or ports60. 6|, 6!, 66 and 64 which are formed in the wall of bore 41. Port 50is connected to the left end of cylinder 26 by a channel 55 and it isconnected to port 64 by a passage 56 formed in body 46. Port II isconnected to drain at all times. Port 62 is connected to the right endof cylinder 26" by a channel 61. Port 53 is supplied at all times withmotive liquid as presently will be explained.

Liquid for effecting operation of valves .H and i2 and for otherpurposes is supplied by a gear pump 60 which draws liquid from areservoir 6| and discharges it into a branched supply channel 62 whichhas one branch thereof connected to port 53 of pilot valve 45. Gear pump66 and reservoir 6| have been shown separate from pump 8 in order thatthe hydraulic circuit may be clearly illustrated but in practice gearpump 60 is driven in unison with pump 6 and it is arranged within thecasing thereof which ordinarily i mounted directly upon reservoir 6|.

One branch of channel "is connected to the inlet of a relief valve 63having the outlet there-' of connected to a channel 64 which isconnected to channels 9 and lo through two check valves 65 and 66respectively. Gear pump 66 discharges liquid at a rate in excess'ofrequirements and a part of this liquid is discharged through reliefvalve 63 which opens at a predetermined pressure, such as 200 p. s. 1..and enables gear pump 60 to maintain that pressure in channel .62. Someof the liquid discharged into channel 64 is exhausted through a reliefvalve 61 which is connected to channel 64 and discharges into reser-VOlr 6l.- Relief valve 61 is adjusted to'open at a somewhat lowerpressure, such as 180 p. s. i.. and thereby causes gear pump 66 tosupercharge pump 8 at that pressure.

When the hydraulic motor is moving table I.

to cause work fastened thereon to be operated pelled from the dischargechamber or chambers of the motor into channel it faster than it canenter pump 6.

If no. means were provided for permitting escape of liquid expelled intochannel II in excess of the liquid which can enter pump 6, the

u inertia of the table would cause the liquid in the and, when the tablereached the end of a jump. the compressed liquid would expand and causelating movement of the table which is very undesirable. V

In order to avoid rebound of the table, the

present invention provides a circuit unlocking Plunger H has one or moreslots 16 formedtherein to provide restricted communication be- ;tweenport 13 and port 14 when it-is in the position shown in Fig. 14. PlungerII also has formed therein one or more slots 16 which provide restrictedcommunication'betweenport 12 and port 14 when plunger II is. in theposition shown in Fig. 1 but which are blocked when plunger II is in theposition shown in Fig. 14.

Plunger H is adapted to be moved to the position shown in Fig. 14 byliquid supplied to the left end of bore I6 and it is adapted to be movedto the position shown in Fig. 1 either by liquid supplied to the rightend of bore 16 or by a piston fitted in a cylinder 6| which is arrangedupon the right end of body 66 and adapted to be supplied with motiveliquid or to be connected to.

drain as will presently be explained.

The arrangement is such that. when table I is I moving toward the righton a cutting stroke, pump 8 is discharging liquid into channel 9 andplunger II is in its right hand position so that slots IQ are blocked toprevent escape of motive liquid from channel 6. If table I should jumpahead dueto any cause such as the tool breaking out of the cut, liquidwill be expelled from the motor cylinders into the return side of thecircuit in excess of the volume which can enter pump 8 and at least apart of this excess liquid, will flow through slots 18 and channel 11into the gear pump circuit. thereby preventing the pressure in thereturn side of the main circuit from becoming high enough to causethetable to rebound at the end of the jump.

. When pump 6 is adjusted to neutral, no liquid will be deliveredthereby but if its displacement varying member should wander slightlyfrom its discharge chamber or chambers to be compressed the table torebound, thereby setting up an oscilcreeping due to pump 8 not beingexactly at zero displacement.

Pump 8 may be of any suitable type but it has been indicated as being ofthe general type shown in Patent No. 2,227,814. Since such pumps arewell known and in extensive use, it is deemed sufficient to state hereinthat the pump has its pumping mechanism arranged within a displacementvarying member or slideblock 82 (Fig. 2') which is arranged within thecasing 83 of the pump, that pump displacement will be zero when theslideblock 82 is in its central or neutral position, and that the pumpwill deliver liquid in a direction and at a rate dependent upon thedirection and distance slideblock 82 is shifted from its neutralposition.

slideblock 82 is continuously urged upward in respect to the drawing, aswill presently be explained, and it is adapted to be moved downward orpermitted to be moved upward in response to operation of a control whichis illustrated in Fig. 2 and is arranged upon the upper side of the pumpin respect to that figure.

This control includes a cylinder 84, which is formed in the sidewall ofpump casing 83, and a piston 85 which engages slideblock 82 and isfitted in cylinder 84 to form therewith a servomotor for shiftingslideblock 82 downward. Cylinder 84 is closed at its outer end by a head86 having a bore 81 formed therein in axial alignment with a bore 88which extends through piston 85 and through an extension or hub 89formed upon the outer face of piston 85. The inner end of bore 88communicates at all times with the interior of casing 83 as by means ofa slot 98 formed in slideblock 82.

Liquid is adapted to flow into and out of cylinder 84 through a port 9|which extends through the wall of hub 89 into communication with bore88. Port 9| is controlled by a rotary valve member 92 which i closelyfitted in bores 81 and 88 and has two spiral grooves 93 and 94 formed inits peripheral surface at opposite sides of port 9| and spaced apart adistance equal to the diameter of port 9|.

One end of groove 93 extends to the end of valve member 92 so thatgroove 93 is at all times in communication with the inner end of bore88. Groove 94 communicates with one end of an internal passage 95 whichextends through valve member 92 and has its other end in communicationwith an annular groove 96 which is formed 1 in the wall of bore 81.Groove 96 communicates with a channel 91 which is fastened to head 86 Iand is adapted to be supplied with motive liquid at a substantiallyconstant pressure as will presently be explained.

Valve member 92 is adapted to be rotated by a lever 98 which is fixed tothe outer end thereof and also restrains valve member 92 from axialmovement. In order to simplify the drawing,

. lever 98 has been shown as being manually operable which wouldnecessitate arranging pump 8 near the operator's station alongside tableI so that lever 98 would be within reach of the operator but in practicepump 8 is arranged in a move convenient location and lever 98 isconnected by linkage to a manually operable lever which is arranged atthe operators station and provided with means for retaining it in anyadjusted position.

The arrangement is such that, when channel 91 is supplied with motiveliquid and groove 94 registers with port 9|, liquid may flow fromchannel 91 through groove 99, passage 95, groove 94 and port 9| intocylinder 84 and, when groove 83 registers with port 9|, liquid mayescape from cylinder 84 through port 9|, groove 93, the inner end ofbore 88 and slot 90 into pump casing 88.

In order that liquid may be permitted to escape from cylinder 84independently of valve member 92, the interior'of cylinder 84 isconnected to channel 91 by a channel 99 having arranged therein a checkvalve I08 which permits liquid to flow from cylinder 84 into channel 91but prevents fiow of liquid from channel 91 into cylinder 84 exceptthrough valve member 9-2.

The pump control thus far described is in extensive use and is knowncommercially as a DH" control. Therefore, the control as an entirety hasbeen designated by the reference character DHI.

In order for a DH control to function, the slideblock must be urgedtoward it by a spring or other means such as a simple hydraulicservomotorwhich is continuously supplied with liquid at a constantpressure as shown in Patent 2,227,814. In the present instance howeverslideblock 82 is urged toward control DHI by a second DH control whichhas been designated by the reference character DH2 and which is the sameas control DHI except that its cylinder 84 and piston 85 are smallerthan cylinder 84 and piston 85, its valve member 92 is provided on itsouter end with a knob |8| for rotating it to adjusted positions and itsgroove 96- has a branch of gear pump supply channel 82 connected theretoso that it is continuously supplied with liquid at a substantiallyconstant pressure. Therefore, like parts have been indicated by likereference numerals with the exponent "(4 added to the reference numeralsapplied to the parts of control DH2 and further description thereof willnot be given. Knob |0| ordinarily is provided with suitable graduationsto indicate the angular position 40 of valve member 92".

Before starting the drive in operation, knob |8| is so adjusted thatgroove 94 is open to port 9| when slideblock 82 is in its neutralposition so that the pressure of the liquid in channel 82 can 45 extendtherefrom through groove 96, passage 95, groove 94 and port 9| intocylinder 84" and cause piston 85 to urge slideblock 82 upward.

However, since piston 85 is smaller than piston 85, it cannot moveslideblock 82 upward as long 60 as liquid is supplied to or trapped incylinder 84 but it will move slideblock 82 upward when cylinder 84 isconnected to exhaust.

Then when channel 91 is supplied with motive liquid and lever 98 isswung toward the right from 65 its neutral position to rotate valvemember 92 clockwise in respect to Fig. 3, groove 94 will open to port 9|and liquid will flow from channel 91 through groove 96, passage 95,groove 94 and port 9| into cylinder 84 and cause piston 85 to move 60slideblock 82 downward in respect to the drawing.

It should be mentioned at this point that grooves 93 and 94 are not truespirals but each consists of two spiral end portions and a short centralportion which extends circumferentially 65 of valve member 92 andconnects the two spiral portions to each other. The centralcircumferential portions of the two grooves 93 and 94 are so locatedthat port 9| is between them and is midway between the ends thereof whenvalve 70 member 92 is in its neutral position.

The arrangement is such that valve member 92 need not be returnedexactly to its neutral position in order to cause slideblock 82 to bereturned exactly to its neutral position. Consequently,

18 valve member 92 must be rotated through a few degrees in onedirection or the other from its neutral position to open groove 83 orgroove 94 to port 9| to thereby cause slideblock 82 to be moved in onedirection or the other from its neutral position but as soon as one ofthe grooves opens toport 9| the movement'of slideblock 82 will beproportional to the rotary movement of valve member 92.

Moving slideblock 82 below its neutral position causes pump 8 todischarge liquid into channel 9 at a rate proportional to the distanceslideblock 82 is moved below its neutral position. Piston 85 will moveslideblock 82 downward until port 9| moves out of registry with groove94 to cut of! flow of liquid to cylinder 84 and thereby stop furthermovement of slideblock 82. Therefore, the distance that slidebock 82 ismoved below its neutral position and the rate at which pump 8 dischargesliquid into channel 9 is determined by the position of control lever 98.

Piston 85 will move downward with slideblock 82 and it will eject liquidfrom its cylinder 84 either throu h port 9|, groove 94, passage 95 andgroove 96 into channel 62 or through channel 99 and check valve I88 intochannel 62 until port 9| moves out of registry with groove 94 and thenit will eject liquid from cylinder 84 through channel 99 and check valveI88 into channel 62.

When channel 91 is disconnected from the source of motive liquid andconnected to a low pressure exhaust as will presently be explained,liquid will flow from channel 62 throughgroove 96 passage 95, groove 94and port 9| into cylinder 84 and cause piston 85 to move slideblock 82upward in respect to the drawing.

Moving slideblock 82 above its neutral position causes pump 8 todischarge liquid into channel I8 at a rate proportional to the distanceslideblock 82 is moved above its neutral position. Piston 85 will moveslideblock 82 upward until port 9| moves out of registry with groove 94to cut off flow of liquid to cylinder 84 and thereby stop furthermovement of slideblock 82. Therefore, the distance that slideblock 82 ismoved above the neutral position is proportional to the angular distancethrough which knob I8I is moved from its neutral position and the rateat which pump 8 discharges liquid into channel I8 is determined by theposition of knob I8I. Piston 85 will move upward with slideblock 82 andit will eject liquid from cylinder 84 through channel 99, check valveI88 and channel 91 to exhaust.

When channel 91 is supplied with motive liquid and lever 98 is swungtoward the left from its neutral position to rotate valve member 92counterclockwise in respect to Fig. 3, groove 93 will open to port 9| sothat liquid can escape from cylinder 84 through port 9|, groove 93, bore88 and slot 98 into pump casing 83 and thereby permit servo-motor 84 -85to move slideblock 82 upward until port 9| moves out of registry withgroove 93 to cut off further escape of liquid from cylinder 84 or untilport 9 I moves out of registry with groove 94 and cuts off further flowof liquid into cylinder 84.

Channel 91' is adapted to be suppl ed with motive l'quid through ahydraulically operated valve I I8 which includes a valve body III havingan axial bore II2 formed therein and a valve or plunger II3 fitted inbore II2 to control communication between three annular grooves or portsH4, H5 and H6 formed in the wall of bore II2. Port II4 has a branch ofgear pump supply 10 channel 62 connected thereto and port H8 has channel91 connected thereto so that control DHI is continuously supplied withgear pump liquid through channel 91 when plunger H3 is in its right handposition as shown in Fig. 1.

When plunger 3 is in its left hand position as shown in Fig. 7, channel91 is adapted to be connected to gear pump supply channel 62 and toexhaust alternately by a pilot valve 1 which includes a valve body II8having an axial bore II9 formed therein and a valve or plunger I28fitted in boreII9 to control commun cation between flve annular groovesor ports I2I, I22, I28,

- its ends by a channel I21 to the left end of bore 18 of valve 68. PortI 23 is connected by a channel I28 to the right end of bore 18 in valve68. Ports I24 and I25 are connected to each other by a passage I29 whichis formed in body I I8 and is connected by a channel I38 to the inlet ofa low pressure relief valve I3I which discharges into reservoir BI andis adapted to open at a low pressure such as 5 p. s. i.

The arrangement is such that, when valve plunger H3 is in its left handpos tion as shown in Fig. 7 and valve plunger I28 is in its left handposition as shown in Fig. 1, pressure will extend from gear pump supplychannel 62 through valve I I1, channel I26, valve I I8 and channel 91 tocontrol DHI to energize it. Pressure will also extend from channel I26through channel I21 to the left end of bore 18 of valve 68 and, if atthat time cylinder 8| is open to drain, plunger 1| will be moved towardthe right and will expel liquid from the right end of bore 18 throughchannel I28, valve II1, channel I38 and relief valve I3I into reservoir6 I.

When valve plunger H3 is in its left hand position as shown in Fig. '7,moving valve plunger I28 to its right hand position as shown in Fig. 6establishes communication between channel 91 and exhaust channel I38 andthereby permits piston of control DH2 to move pump slideblock 82 upwardand cause piston 85 of control DHI to eject liquid from cylinder 84through channel 99, check valve I88, channel 91, valve II8, channel I26,valve II1, channel I38 and relief valve I3I which resists the dischargeof liquid therethrough and thereby prevents sl deblock 82 fromoverrunning when movement of piston 85' ceases. Also, liquid will flowfrom gear pump supply channel 62 through valve II 1 and channel I28 tothe right end of bore 18 in valve 68 and cause plunger H to move towardthe left and eject liquid from the left end of bore 18 through channelsI21 and I26, valve II1, channel I38 and relief valve I 3|.

Plunger I28 of valve I I1 is adapted to be shifted from one to the otherof its two positions by a reversing mechanism operable in response totable I reaching one end or the other of a predetermined stroke.

The reversing mechanism may assume various forms but, as shown, valveplunger I28 has its stem connected to one arm of a bell crank lever I 35which is pivoted upon a stationary shaft I36 and has its other armconnected by link I31 to one end of a lever I38 having the other endthereof mounted upon a shaft I39 which is arranged in a stationaryposition. Shaft I89 also has mounted thereon two reversing ears I40 andI which are fixed for rotation with lever I38 and have the ends thereofextending into the paths of two dogs I42 and I43 which are fastened totable I in adjusted positions.

when dog I42 engages ear I40 during movement of table I toward the left,it will cause the reversing mechanism to shift valve plunger I20 to theposition shown in Fig. l and, when dog I43 engages ear I during movementof table I toward the right, it will cause the reversing mechanism toshift valve plunger I20 to the position shown in. Fig. 6. Thus, when thedrive is operating, table I normally reciprocates within a fixed rangeas determined by the positions of dogs I42 and I43.

It is necessary at times to move table I beyond its normal range ofreciprocation for the purpose of replacing or inspecting the work upontable I. In order that this may be accomplished without furtheradJustment of the dogs or the reversing ears, plunger II3 of valve IIOmust be shifted to the position shown inFig. 1 to prevent pilot valveII! from effecting operation of pump control DHI, and servo-motor 808Ishould shift plunger II of valve 68 to the position shown in Fig. 1 toprevent bypassing any of the liquid discharged by pump 8 into channelI0.

Valve plunger H3 is adapted to be shifted in one direction or the otherby liquid delivered to one end or the other of bore II2 through one orthe other of two channels I48 and I49 which are connected to oppositeends of body III. A branch of channel I49 is connected to cylinder 8| onvalve 68 so that, when liquid is supplied thru channel I49 to shiftplunger II3 to the position shown in Fig. 1, servo-motor 80-8I will beenergized and will shift valve plunger 'II to the position shown inFig. 1. The flow of liquid through channels I48 and I 49 is under thecontrol of a valve I50 which is operable in unison with con trol lever98.

Valve I50 may be an individual valve which is connected to lever 98 tobe operated thereby. However, in order to provide a compact control,valve I 50 preferably is provided by forming ports and passages incylinder head 86 and in valve member 92 of control DHI but functionally,it is Just as independent of control DHI as if it were a separatestructure.

As shown in Figs. 2-5, channels I48 and I49 and a branch of gear pumpsupply channel 62 are connected to head 86 and communicate with bore 81in a plane situated between port 96 and an annular groove or drain portI 5| which is formed in the wall of bore 81 and communicates with achannel I52 which discharges into reservoir 6|. Channel 62 is adapted tobe connected to channel I48 and I49 selectively by two circumferentialgrooves I53 and I54 which are formed in the peripheral surface of valvemember 92 and are'connected to each other by an internal passage I55formed in valve member 92. Drain port I5l is adapted to be connected tochannels I48 and I49 alternately by a circumferential groove I56 whichis formed in the peripheral surface of valve member 92 between theadjacent ends of grooves I53 and I54 and is wide enough to communicatewith port I5I. The portions of valve member 92 and head 86 axiallyoutward from port 96 thus constitute valve I50.

The arrangement is such that, when lever 98 is moved to its neutralposition as shown in Fig. 3 or is swung toward the left beyond itsneutral position as shown in Fig. 5, groove I53 will com- 12 municatewith channel I49 and groove I56 will communicate with channel I48 sothat liquid can flow from channel 62 through groove I53 and channel I49to valve H0 and cause its plunger II3 to move toward the right and toeject liquid from the right end of bore 1 I2 through channel I48 andgroove I56 into drain port I5I. Also,

liquid will flow through the branch of channel I49 tocylinder 8| andcause piston 80 to move valve plunger II to the position shown in Fig.1.

When lever 98 is swung toward the right a predetermined distance beyondits neutral position as shown in Fig. 4, groove I54 will communicatewith channel I 48 and groove I56 will communicate with channel I49 sothat liquid can flow from channel 62 through groove I53, passage I55,groove I54 and channel I48 to valve I I0 and cause its plunger II3 tomove toward the left and to eject liquid from the left end of bore I I2through channel I49 and groove I56 into drain port I5I.

OPERATION Assuming that table I has been moving toward the right atmedium speed and that control lever 98 has been returned to its neutralposition to cause control DHI to adjust pump 8 to neutral and therebystop table I, the plungers of the several valves will be in thepositions shown in Fig. 1.

With both pumps running, any liquid which might be discharged by pump 8will be discharged thru channel 9 and be bypassed through valve 68, andgear pump 60 will be discharging through relief valves 63 and 61 intoreservoir M. The resistance offered by relief valve 61 enables pump 60to maintain pressure in both sides of the main circuit to keep itflooded and the resistance offered by relief valve 63 enables gear pump60 to maintain pressure at both ends of valve 68, to maintain pressurein cylinder 26 to enable piston 25 to hold plunger 23 of valve II to theright, to maintain pressure in cylinder 26 to enable piston 25 to holdplunger 23 of valve I2 to the left, and to maintain pressure at theright end of valve H0 to hold plunger II3 to the right.

Operation at medium speed The drive may be started by swinging lever 98toward the right from its neutral position to thereby rotate valvemember 92 clockwise in respect to Fig. 4. As soon as valve member 92 isrotated through a short angular distance from its neutral position,pressure groove I54 will open to channel I48 and drain groove I 56 willopen to channel I49, as shown in Fig. 4, which will connect cylinder 8|and the left end of valve I III to drain and permit gear pump liquid toshift valve plunger II of valve 68 to the position shown in Fig. 14 andalso permit gear pump liquid to shift plunger II3 of valve IIO to theposition shown in Fig. 7 to thereby enable pilot valve II! to controlthe flow of liquid to and from control DHI as previously explained.

As soon as valve member 92 has been' rotated far enough to open groove94 to port 9|, gear pump liquid will enter control DHI and cause it tomove slideblock 82 downward in respect to the drawings to'a positioncorresponding to the position of lever 98 and thereby cause pump 8 todischarge liquid into channel 9 as previously explained. The liquiddischarged by pump 8 will flow through channels 9 and 35, valve I2,check valve 43 and channel 4| to the rod end of cylinder 2 and causepiston 3 to start table I moving toward the right.

15 The rate at which pump 8 discharges liquid toward the right withtable 'I.

toward the right will gradually increase until movement of control lever88 toward the right ceases and then table I will be moving toward theright on a cutting stroke at a medium speed determined by the positionof control lever 88 and the area of piston 8 upon which the liquid acts.

As piston 8- moves table v will eject liquid from the right end ofcylinder 2 into return channel II. A part of the ejected liquid willflow from channel I8 through channels 88 and 81, valve II, check valve48 and channel 88 to cylinder 8 to keep it flooded as ram 8 moves Theremainder of the ejected liquid will flow through channel II to theintake of pump. 8. Table I will continue to'move toward the right untildog [Ill operates reversing mechanism Iii-Ill to shift the plunger I28of valve III to the right .to the position shown in Fig. 6 which willdisconnect channel I28 from gear pump supply channel 82 and connect itto exhaust channel III to thereby enable control DB2 to move slideblock82 upward and cause pump 8 to discharge liquid into channel II at therate determined by the adjustment of knob III as previously explained. I

Shifting plunger I28 of valve III to the right also connects supplychannel 82 to channel I28 so that liquid will flow therethrough to valve88 and move plunger II toward the left to the position shown in Fig. 15to thereby prevent pump 8 from discharging into the gear pump I circuit.

The liquid discharged by pump 8 into channel I I will flow therethroughto the head end of cylinder 2 and cause piston! to move table I towardthe left on a return stroke.

As table I moves toward the left, piston 3 will eject liquid fromcylinder 2 mm channel u and ram-8 will eject liquid from cylinder intochannel 88. The liquid ejected by piston 3 into channel II will flowtherethrough and through channel 82 to the left end'of valve I2 and'moveits plunger 28 toward the right to the position shown in Fig. 9 and thenthe liquid will flow throughvalve I2 and channels '31 and 88 intochannel II where it joins the liquid discharged by pump 8 so that pump 8must supply'only a volume of liquid equal to the displacement of pistonrod 4. Therefore, table I will be moved toward the left at a highspeedwhich isdetermined by the adjustment of pump control DH2 and thearea of pistonion which the liquid acts. The liquid ejected by ram 8into channel 38 will I flow therethrough and through channel 38 to thenel I21 and shift the plunger II of valve 88 to the position shown inFig. 14 and also permit gear pump liquid to flow through channel 81 tocontrol DHI and cause its piston 85 to move slideblock 82 downward tothe position determined by the position of control lever '88, therebyreversing the flow from pump 8. 7

Assoonastheflowisreversed,spring 21 will move plunger 23 of valve II tothe position I toward the right; it

- 14 shown inl'ig. 1 and v 28' of valve I2 to the position shown inFig. 1. Then theliquid discharged by pump 8 will flow to cylinder 2 andcause piston 3 to move table Operationat low speed If the parts are inthe positions shown in Fig. 1 and it is desiredthat the drive beoperated within a low speed range, plunger 48 of valve 48 is shifted tothe position shown in Fig. 12 to connect cylinder 28 to drain and permitspring 24 to shift plunger 23 of valve II to the position shown in Fig.10.

Thenwhen control lever 98 is moved toward the right from its neutralposition as indicated in Fig. 4, the drive will operate in the samemannet as when adjusted for operation within a medium speed range and asexplained above except that the liquid discharged by pump 8 intochannels 8 and will flow therefrom through valve II and channel 88 tocylinder 5 in addition to flowing through valve I2 and channel ll to therod end of cylinder 2. The liquid discharged by pump 8 will thus actupon the end of ram 8 in addition to acting upon the left side of piston8 so that table I will be moved toward the right at a low speeddetermined by the position of control lever 88 and the total ram andpiston area upon which the liquid acts.

As table I moves toward the right, piston 8 will eject liquid fromcylinder 2 and the ejected liquid will flow through channel I8 to theintake of pump 8.

Table I will move toward the right at low speed until dog I48 operatesreversing mechanism I85-III to effect reversal and then table I willmove toward the left at high speed until dog I42 operates reversingmechanism I35--I4I to Operation at high speed If the parts are in thepositions shown in Fig. l and it is desired that the drive be operatedwithin a high speed range, plunger 48 of valve 45 is shifted to theposition shown in Fig. 13 to connect cylinders 26 and 26 to drain andpermit springs 28 and 24 to shift valve plungers 23 and 28"- to thepositions shown in Figs. 8 and 10 respectively.

Then when control lever 98 is moved toward the right from its neutralposition as indicated in Fig. 4, the drive will operate in the samemanner as when adjusted for operation within a medium speed range and asexplained. above except that the liquid discharged by pump 8 intochannels 8 and 85 will flow therefrom through valve II and channel 38 tocylinder 5 and cause ram 6 to move table I toward the right at a highspeed determined by the position of control lever 88 and the area of ram6.

As table I' moves toward the right, piston 3 will eject liquid from thehead end of cylinder 2 into channel III. A part of the ejected liquidwill flow from channel I8 through channels 88 7s and 81. valve I2 checkvalve 43 and channel ll spring 21 will move plunger to the rod end ofcylinder 2 to keep it flooded and the remainder of the ejected liquidwill flow through channel III to the intake of pump 8.

Table I will move toward the right athigh speed until dog I43 operatesreversing mechanism I35-I4I to effect reversal andthen table I will movetoward the left at high speed until dog I42 operates reversing mechanismI85--I4I to cause table I to again move toward the right as explainedabove. Table I will continue to reciprocate in this manner until thedrive is stopped or its operation altered by the operator.

Manual control The movements of table I may be removed from under thentrol of pilot valve II! and brought under the control of the operatorat any time by merely moving control lever 98 toward its neutralposition until port I53 opens to channel I49 and port I56 opens tochannel I48 which will cause gear pump liquid to flow from channel 82through valve I50 and channel I49 to valve H and move its plunger 3 tothe position shown in Fig. 1 so that control DHI is continuouslysupplied with ear pump liquid.

If lever 98 is a substantial distance toward the right from its neutralposition and pilot valve plunger I 20 is in the position shown in Fig. 1so that table I is moving toward the right, moving lever 98 toward theleft will open groove 93 to port 9I (Fig. 2) to permit piston 85 to moveslideblock 82 upward and thereby reduce the displacement of pump 8 andconsequently decelerate table I at a rate proportional to the rate atwhich lever 98 is moved but if pilot valve plunger I20 is in theposition shown in Fig. 6 so that table I is moving toward the left,channel 91 will be open to exhaust channel I30 and table I will continueto move toward the left until dog I42 operates the reversing mechanismto shift pilot valve plunger I20 to the position shown in Fig. 1 oruntil lever 98 has been moved far enough to cause plunger H3 of valveIII} to be shifted to the position shown in Fig. 1. Thereafter, thedisplacement of pump 8 and the movement of table I are solely under thecontrol of lever 98 as long as lever 98 is not moved far enough towardthe right to open groove I56 to channel I49 and groove I54 to channelI48.

If it is desired to retract tabl I' beyond its normal range ofreciprocation, lever 98 may be moved toward the left from its neutralposition which will cause pump 8 to discharge liquid into channel I0 andtable I to move toward the left at a rate determined by the position oflever 98 as previously explained. As table I moves toward the left, dogI42 will operate the reversing mechanism to shift pilot valve plungerI20 which will have no effect at this time for the reason that valveplunger I I3 is in the position shown in Fig. 1 so that control DHI iscontinuously supplied with motive liquid.

Control lever 98 thus may be operated to start, stop and reverse thetable, to move the table in either direction, to cause the 'table toreciprocate continuously within a predetermined range, to change thespeed of the table and to move the table to a desired position outsidthat range.

The hydraulic drive described herein may be modified in various wayswithout departing from the scope of the invention which is herebyclaimed as follows:

1. In a machine having an element adapted to be moved in one or theother of two directions selectively, the combination of hydraulic motormeans connected to said element and having three pressure chambers ofdifferent capacities, a pump for supplying motive liquid to said motormeans to energize the same, channel means connecting said pump and saidmotor means and forming therewith a hydraulic circuit, valve meansarranged in said circuit and shiftable to different positions to causeliquid to flow from said pump to either one of the two smaller of saidchambers and liquid to flow from the largest one of said chambers to theother one of the two smaller of said chambers or to cause liquid to flowfrom said pump to both of the two smaller of said chambers and liquid toflow from the largest one of said chambers to said pump to thereby causesaid motor means to move said element in one direction at any one ofthree different speeds, means for reversing the flow in said circuit tothereby cause said motor means to move said element in the oppositedirection, hydraulic means for shifting said valve means, means forsupplying operating liquid to said hydraulic means including a pilotvalve for directing said operating liquid to and from said hydraulicmeans selectively, and means operated by said element during itsmovement in each direction for effecting operation of said reversingmeans.

2. In a machine having an element adapted to be moved in one or theother of two directions selectively, the combination of hydraulic motormeans connected to said element and having three pressure chambers ofdiiferent capacities, a pump for supplying motive liquid to said motormeans to energize the same, channel means connecting said pump and saidmotor means and forming therewith a hydraulic circult, valve meansarranged in said circuit and shiftable to different positions to causeliquid to flow from said pump to either one of the two smaller of saidchambers and liquid to flow from the largest one of said chambers to theother one of the two smaller of said chambers or to cause liquid to flowfrom said pump to both of the two smaller of said chambers and liquid toflow from the largest one of said chambers to said pump to thereby causesaid motor means to move said element in one direction at any one ofthree different speeds, means for reversing the flow in said circuit tothereby cause said motor means to move said element in the oppositedirection, hydraulic means for shifting said valve means, means forsupplying operating liquid to said hydraulic means including a pilotvalve for directing said operating liquid to and from said hydraulicmeans selectively, said valve means being responsive to said reverseflow for directing said motive liquid to a predetermined pressure areaof said motor, and means operated by said element during its movement ineach direction for effecting operation of said reversing means.

3. In a machine having an element adapted to be moved in oppositedirections selectively, the combination of hydraulic motor means whichincludes a first cylinder having a piston fitted thereinand connected tosaid element by a piston rod and a second cylinder having a ramextending into it and connected to said element, a pump. fluid channelsconnecting said pump to said motor means and forming therewith ahydraulic circuit, and valve means arranged in said circuit and adaptedto connect said pump either to said second cylinder or to the rod end ofsaid first cylinder or to both said second cylinder and the rod end ofsaid first cylinder to cause said motor means to advance said element atany one of three different speeds or upon reversal of now in saidcircuit to connect said pump to both ends of said first cylinder tocause said motor means to retract said element at high speed.

4. In a machine having an element adapted to be moved in one or theother of two directions selectively, the combination of hydraulic motormeans connected-to said element and having a plurality of pressureareas, a pump for supplying motive liquid to said motor means toenergize the same and having hydraulic means for varying itsdisplacement, a source of operating liquid, means for supplying liquidfrom said source to said hydraulic means including a control valve fordirecting said liquid thereto and therefrom, channel means connectingsaid pump and said motor means and forming therewith a hydrauliccircuit, valve means arranged in said circuit and shiftable to diflerentpositions to direct liquid from said pump to one or more of saidpressure areas to thereby cause said motor means to move said element atany one of a plurality of speeds, means for adjusting said valve meansto selected positions, hydraulically operated meansfor reversing theflow in said circuit to thereby efiect reversal of said element, meansfor supplying liquid from said source to said reversing means includinga reversing valve for connecting said means to said source and toexhaust alternately to thereby efiect reversal of fiow in said circuit,means operated by said element during its movement in each direction forefiecting operation of said reversing valve, a hydraulically operatedvalve shiftable from one to the other of two positions to render saidreversing valve efiective or ineffective to effect operation of saidreversing means, means for supplying liquid to said hydraulicallyoperated valve to efiect operation thereof including a manually operablevalve, and a control element for operating the last mentioned valve andsaid control valve simultaneously;

5. A hydraulic drive according to claim 4 in which the control valve andthe manually operable valve include rotary valve elements which areformed integral with each other and the control element is connectedthereto.

6. A hydraulic drive according to claim 4 provided with an unlockingvalve which is connected to both sides of said hydraulic circuit and isshiftable from one to-the other of two positions in each of which itprovides a restricted passage for the escape of liquid from that side ofthe circuit into which liquid is discharged by the motor means, saidunlocking valve being shiftable from one to the other of its twopositions in response to said reversing valve being shifted from one tothe other of its two positions.

7. A hydraulic drive according to claim 4 in which said motor meansincludesa first cylinder having a piston fitted therein and connected tosaid element by a piston rod and a second cylinder having a'ramextending into it and connected to said element, and in which said valvemeans is adapted to connect said pump either to said second cylinder orto the rod end of said first. cylinder or to both said second cylinderand the rod end of said first cylinder to cause said motor means toadvance said element at any one of three diflerent speeds or uponreversal of flow in said circuit to connect said pump to both ends ofsaid first cylinder to cause said motor means to retract said element athigh speed. 7

8. A hydraulic drive according to claim 4 in which said manuallyoperable valve is effective to cause said hydraulically operated valveto be shifted only when said control valve is adjusted to effectreduction of pump delivery to a predetermined minimum.

9. In a machine having an element adapted to be moved in one or theother of two directions selectively, the combination of hydraulic motormeans connected to said element and having a plurality of pressureareas, a pump for supplying motive liquid to said motor means toenergize the same and having a member shiftable in opposite directionsfrom a neutral position to vary the rate and direction of pump delivery,channel means connecting said pump and said motor means and formingtherewith a hydraulic circuit,

tions, a servo-motor for efiecting movement of,

said displacement varying member, a source of operating liquid, meansfor supplying liquid from said source to said servo-motor including aconrol valve to direct said liquid thereto and therefrom and a reversingvalve for controlling the flow of liquid to said control valve and fromsaid servo-motor and adapted when shifted from one to the other of twopositions to cause said servomotor to shift said displacement varyingmember and thereby reverse the flow in said circuit, means operated bysaid element during its movement in each direction for effectingoperation of said reversing valve, a hydraulically operated valveshiftable from one to the other of two positions to render saidreversing valve eifective or inefiective to control said flow of liquid,means for supplying liquid to said hydraulically operated valve toeffectoperation thereof including a manually operable valve, and a controlelement for operating the last mentioned valve and said control valvesimultaneously.

10. A hydraulic drive according to claim 9 in which the control valveand the manually operable valve include rotary valve elements which areformed integral with each other and the control element is connectedthereto.

11. A hydraulic drive according to claim 9 pro-' vided with an unlockingvalve which is connected to both sides of said hydraulic circuit and isshiftable from one to'the other of two positions in each of which itprovides a restricted passage for the escape of liquid from that side ofthe circuit into which liquid is discharged by the motor means, saidunlocking valve being shiftable from one to the other of its twopositions in response to said reversing valve being shifted secondcylinder or to the rod end of said first cylinder or to both said secondcylinder and the rod end of said first cylinder to cause said motormeans to advance said element at any one of three different speeds orupon reversal of flow in said circuit to connect said pump to both endsof said first cylinder to cause said motor means to retract said elementat high speed.

13, In a machine having an element adapted be moved in one or the otherof two directions selectively, the combination of hydraulic motor meansfor reciprocating said element, a pump for supplying motive liquid tosaid motor means to energize the same, channel means connecting saidpump and said motor means and forming therewith a hydraulic circuithaving two sides each of which functions alternately as a pressure sideand a return side, a hydraulically operated unlocking valve arrangedoutside said circuit and connected to both sides thereof, said unlockingvalve being shiftable to two positions in each of which it blocks escapeof liquid from the pressure side of said circuit and provides arestricted passage for the escape from the pressure side of said circuitof liquid discharged by said motor means in excess of the liquid whichcan enter said pump, means for reversing the flow in said circuit tothereby effect reversal of said element, and a hydraulic servo-motor foroperating said reversing means, and a pilot valve operated by saidelement for controlling the operation of both said servo-motor and saidunlocking valve.

14. In a machine having an element adapted to be moved in one or theother of two directions selectively, the combination of hydraulic motormeans for reciprocating said element, a pump for supplying motive liquidto said motor means to energize the same, channel means connecting saidpump and said motor means and forming therewith a hydraulic circuit,means for reversing the flow in said circuit to thereby effect reversalof said element, means for reducing the flow in said circuit to aminimum to thereby decelerate said element to a low speed, an unlockingvalve connected to both sides of said circuit and shiftable to twopositions in the first of which it provides a restricted passage throughwhich liquid may escape from one side of said circuit and in the secondof which it provides a restricted passage through which liquid mayescape from the other side of said circuit, means responsive tooperation of said reversing means for shifting said unlocking valve fromone to the other of its two positions, and other means responsive tooperation of saidilow reducing means for shifting said unlocking valveto its second position.

15. In a machine having an element adapted to be moved in one or theother of two directions selectively, the combination of hydraulic motormeans for reciprocating said element, a pump for supplying motive liquidto said motor means to energize the same, channel means connecting saidpump and said motor means and forming there'- with a main hydrauliccircuit, means for reversing the flow in said circuit to thereby'efiectreversal of said element, means operated by said element during itsmovement in each direction for effecting operation of said reversingmeans, means for reducing the flow in said circuit to a minimum tothereby decelerate said element to a low speed, an auxiliary circuit,means for supplying liquid to saidauxiliary circuit at a predeterminedpressure, means connecting said auxiliary circuit to both sides of saidmain circuit to maintain a predetermined back pressure on said motormeans and to supercharge said pump, an unlocking valve connected to saidauxiliary circuit and to both sides of said main circuit and shiftableto two positions in the first of which it provides a restricted passagethrough which liquid 7 may escape from one side of said main circuitinto said auxiliary circuit and in the second of which it provides arestricted passage through which liquid may escape from the other sideof said main circuit into said auxiliary circuit, means responsive tooperation of said reversing means for shifting said unlocking valve fromone to the other of its two positions, and other means responsive tooperation of said flow reducing means for shifting said unlocking valveto its second position.

16. In a machine having an element adapted to be moved in one or theother of two directions selectively, the combination of hydraulic motormeans connected to said element and having a plurality of pressureareas, a pump for supplying motive liquid to said motor means toenergize the same, channel means connecting said pump and said motormeans and forming therewith a hydraulic circuit, valve means arranged insaid circuit and shiftable to different positions to ,direct liquid fromsaid pump to one or more of said pressure areas to thereby cause saidmotor means to advance said element at any one of a plurality of speeds,hydraulic means for shifting said valve means, means for supplyingoperating liquid to said hydraulic means including a pilot valve fordirecting said operating liquid to and from said hydraulic meansselectively, an unlocking valve connected to said circuit and adapted inone position to provide a restricted passage for the escape from saidcircuit of liquid discharged by said motor means in excess of the liquidwhich can enter said pump, means for reversing the flow in said circuitto thereby effect reversal of said element, and means responsive tooperation of said reversing meansfor shifting said unlocking valve toanother position.

17. In a machine having an element adapted to be moved in one or theother of two directions selectively, the combination of hydraulic motormeans for reciprocating said element, a pump for supplying motive liquidto said motor means to energize the same and having hydraulic means forvarying its displacement, a source of operating liquid, means forsupplying liquid from said source to said hydraulic means including acon trol valve for directing said liquid thereto and therefrom, channelmeans connecting said pump and said motor means and forming therewith ahydraulic circuit, means for reversing the flow in said circuit tothereby effect reversal of said element, means operated by said elementduring its movement in each direction for efiecting operation of saidreversing means, an unlocking valve connected to both sides of saidcircuit and shiftabl to two positions in the first of which it providesa restricted passage through which liquid may escape from one side ofSaid circuit and in the second of which it provides a restricted p1ssage through which liquid may escape from the other side of saidcircuit, means responsive to operation of said reversing means forshifting said unlocking valve from one to the other of its twopositions, a servo-motor for shifting said unlocking valve to its secondposition, means for supplying liquid from said source to said servomotorincluding a manually operable valve for directing said liquid theretoand therefrom, and a control element for operating the last mentionedvalve and said control valve simultaneously.

18. A hydraulic drive according to claim 17 in v which the control valveand the manually operable valve include rotary valve elements which areformed integral with each other and the control element is connectedthereto.

19. In a. machine having an element adapted to be moved in one or theother of two directions selectively, the combination of hydraulic motormeans connected to said element and having a plurality of pressureareas, a pump for supplying motive liquid to said motor means toenergize the same, channel means connecting said pump and said motormeans and forming therewith a hydraulic circuit, means for reversing theflow in said circuit to thereby effect reversal of said element, meansoperated by said element during its movement in each direction forefiecting operation of said reversing means, two valves arranged in saidcircuit for directing liquid from said pump to one or more of saidpressure areas selectively to thereby cause said motor means to movesaid element at any one of a plurality of speeds, each of said valv sincluding a Valve body having a bore, a valve plunger fitted in saidbore and a light spring in one end of said bore for moving said plungerin one direction, a servo-motor arranged at the other end of said boreand adapted when energized to move said plunger in the oppositedirection, a spring stronger than said light spring arranged in saidservo-motor for permitting said plunger to move in said on directionwhen said servo-motor is energized and the end of said bore containingsaid light spring is supplied with liquid at a pressure higher than thepressure in the other end of said bore, a source of operating liquid,and means including a pilot valve for connecting the servo-motors onboth or said valves to said source and to exhaust selectively.

22 20. A hydraulic drive according to claim 19 in which the plunger ofeach of said valves has upon the end thereof adjacent said servo-motor apiston adapted to enter the end portion of said bore 7 and provided witha slot through which liquid may escape from said end of said bore whensaid plunger is moved in said one direction and through which pressuremay extend to equalize the pressures on opposite ends of said plunger.JAMES K. DOUGLAS.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS.

Number Name Date 1,843,082 Ferris et a1 Jan. 26, 1932 1,983,900 Ferriset a1 Dec. 11, 1934 2,000,805 West et a1 May 7, 1935 2,005,018 West etal June 18, 1935 2,114,005 Tyler Apr. 12, 1938 2,157,240 Keel May 9,1939 2,160,217 Kingsbury May 30, 1939 2,271,615 Bauer Feb. 3, 19422,345,919 Davis Apr. 4, 1944 2,353,791 Shartle July 18, 1944 2,382,452Svenson Aug. 14, 1945 2,389,829 Tyler Nov. 27, 1945 2,397,395 WiedmannMar. 26, 1946

